Method of recovering selective solvents



Patented Aug. 5, 1941 V.

UNlTED STATES r'rsNr orrics METHOD OF RECOVERING SELECTIVE SOLVENTSHendrikus van der Waerden, The Hague, Netherlands, assignor to ShellDevelopment Company, San Francisco, Calif., a corporation of Delaware NoDrawing. Application July 26, 1935, Serial No. 33,315. In theNetherlands August 2, 1934 1 Claim. (01 196-13) This invention relatesto the art of extracting oil-solvent mixture with an extracting agenthydrocarbon mixtures with selective solvents for which is a volatilepolar liquid and is capable separating them into portions which are,respecof dissolving the high boiling selective solvent tively,relatively more paraffinic and more aroin preference to thehydrocarbons. In other matic and/or naphthenio, and is particularlywords, the extracting agent must be more misconcerned with an improvedmethod for removcible with the selective solvent than with the oil, ingthe selective solvent from the hydrocarbons and must be capable offorming two liquid layers in the liquid phases produced in theextraction when mixed with the hydrocarbon-solvent mixprocess. ture. Thevolatile extracting agent can then be In the extraction of hydrocarbonoils relaremoved from the hydrocarbons and from the tively high-boilingselective liquids are often emselective solvent by separately distillingthe ployed as the selective solvent. The quantitative phases from thewashing treatment at a low recovery of the solvent from the hydrocarbonstemperature, and both the selective solvent and is necessitated by thecost of these solvents the extracting agent may be recycled to treatand/or bythe requirement of producing hydrofurther quantities of oil.carbon products which are entirely free from I have found liquid sulfurdioxide to be espethe selective solvent. To accomplish this s'epaciallyuseful as an extracting agent for this Other volatile or low boilingpolar ration by distillation is, however, often not pracpurpose.

tical because of the formation of decomposition, liquids, particularlyfurfurane, acetone, acetaldepolymerization, or reaction products of thehyhyde, and formaldehyde may also be employed. drocarbons and theselective solvent. These un- They should, preferably, have boilingpoints bedesirable reaction products often have an adlow 60 C.

verse influence upon the color and/or other char- Such volatile polarliquids may be used with acteristics of the hydrocarbon products, andare any high boiling selective solvents. Among such generally verydiflicult to separate therefrom. high-boiling solvents may beparticularly men- Moreover, the formation of these undesirable tioned:cresols, phenols, furfural, (furfuraldeproducts entails a loss of thesolvent. As an hyde), nitro-benzene, ,Bfldichloroethyl ether example maybe mentioned the removal of fur- (Chlorex) and aniline.

furol, or cresol, or nitrobenzene, etc., from a The quantity ofextracting agent to be emlubricating oil raflinate. tended withdecolorization and polymerization.

This is generally atployed in a given situation depends upon the mutualsolubility of the three components (hy- If such separations are to beeffected by disdrocarbons, high-boiling selective solvent, andtiliation, not only is it necessary to employ a low-boiling extractingagent) at the temperature high vacuum in the distillation column, but itemployed. The treatment with the low boiling is also necessary tocontrol the conditions in the extracting agent should, preferably, butnot neccolumn with great care to avoid overheating and essarily, beaccording to the countercurrent mode to prevent the exposure of thesolvent to the of operation. It may be carried out in any suitelevatedtemperatures for too long a time. In able liquid contact apparatus, suchas a packed many cases even the use of a high vacuum will column, or asingleor multi-stage countercurnot entirely prevent the deterioration ofthe rent treater, of the type commonly employed in products, and itbecomes necessary to subject extraction processes. This washing of theoilthe hydrocarbons to further refining treatments, solvent solution maybe conducted according to This is especially true of the raffinatesproduced the methods employed in the extraction of liquid in theextraction of lubricating oils. mixtures with selective solvents, andmay employ It has been proposed to avoid the necessity such improvementsthereon as a temperature of distillation by washing the oil-solventmixture gradient, as described in the Netherlands Patent with a lightnaphtha. Since, however, the 27,077; and/or a backwash, as described inthe naphtha is ineffective to remove all of the se- Netherlands Patent33,941. lective solvent, it was often necessary to follow It is,moreover, often desirable to wash the this washing with a furthertreatment of the solution of selective solvent and extracting agent oilwith a chemical which would react with the with a light parafliniohydrocarbon, such as prosolvent and remove the last traces thereof.pane, butane, pentane, or with light naphtha, In accordance with thepresent invention I having a boiling temperature different from thathave found that the selective solvent can be of the hydrocarbon mixturebeing extracted. effectively removed from the oil by washing the Thiswashing is effective in removing the last traces of hydrocarbons fromthe selective solventextracting agent mixture. It should be noted,however, that this expedient is not at all essential because theselective solvent and extracting agent are normally returned to theprocess, and any hydrocarbons contained therein would be returned withthem.

In order to describe my invention more fully, the following example isset forth:

A lubricating oil raffinate phase which was obtained by extracting aVenezuelan raw petroleum fraction with furfural, and which contained 8%furfural, Was completely freedrfrom furfural by a single washing in abatch treatment with 33% by volume (based on the ralfinate phase) ofliquid sulfur dioxide. The use of a countercurrent method of contactwould permitlthe complete removal of the furfural with a substantiallysmaller quantity of sulfur dioxide. The same result was obtained whenwashing a similar rafiinate containing cresol instead of furfural.

The low boiling sulfur dioxide was readily removed from the oilraffinate and from the furfural by distillation at a low temperature.

The oil raffinate, after the distillation to remove the sulfur dioxide,had a much lighter color than that obtained by distilling off thefurfural from the oil raflinate. Consequently, no second refining of therafiinate was required for this product, whereas a raflinate produced bydistilling the'furfural from another portion of the above rafiinatephase had an undesirable color and had to be subjected to furtherrefining.

It'should be noted that although I have described the application of myinvention to the production of a lubricating oil .rafiinate, it is notrestricted thereto, but may be employed as well to the recovery of thesolvent from the extract phase, without departing from the scope of myinvention. My invention may also be applied to the recovery of highboiling selective solvent from hydrocarbons which boil below the boilingtemperature ranges of lubricating oils.

As used in the present specification and claims, the term high boilingselective solvent is intended to include all selective solvents which,at normal pressure, boil at temperatures at which decomposition, and/orpolymerization, and/or reaction with the hydrocarbons occurs, as well asthose which boil at temperatures substantially above 150 C., and more,therefore, diflicult to separate from hydrocarbons without theemployment of vacuum and/or steam distillation methods, although usuallyno undesirable products would be formed in such distillations. Myinvention' isnot, therefore, to be limited to the recovery of thespecific selective solvents heretofore recited, nor to the use of thespecific extracting agents disclosed, but is to be construed ascoveringbroadly the recovery of any high boiling seleotive solvent fromhydrocarbon mixtures.

I-claim as my invention:

The: process of producing a lubricating oil which comprises the steps ofextracting a petroleum lubricating oil with furfural to produce liquidramnate and extract phases separating said phases, contacting saidrafiinate phase with liquid sulfur dioxide'to produce two second liquidphases oneof which is rich in oil and substantially completely freefromfurfural, the other consisting-predominantly'of furfural and sulfurdioxide, separating the said second phases, and

separately removing the liquid sulfur dioxide from the former secondphase by'distillation.

HENDRIKUS 'VAN DER WAERDEN.

